Migrate API backend to SQLite, add MCP layer, and Docker Compose deployment

[guillochon]

Summary

• migrate runtime data loading to a SQLite-backed store while preserving existing API route signatures and query semantics
• add a static ingest pipeline to build oacapi.db from astrocatalog repositories
• remove TNS integration so the API no longer interacts with external services
• add an MCP server layer (mcp_server.py) that reuses API query logic through a shared query service
• add Docker Compose deployment with api, mcp, and ingest services plus Dockerfiles and environment defaults
• remove the astrocats python package dependency by replacing helper usage with local compatibility utilities
• update sqlite storage strategy to store event JSON file pointers (not full event JSON blobs), so full queries read directly from existing output/json files without duplicating ~50G event data
• document deployment/runtime options and add migration smoke tests

Key implementation details

• classes/models.py + classes/sqlite_store.py define SQLAlchemy schema and persistence utilities
• sqlite events rows now include event_path pointer instead of full_json payload
• scripts/ingest_static_catalogs.py records event JSON file paths and resets schema on rebuild
• api.py full-query flow loads full event JSON from event_path (or legacy path resolver) and preserves existing route signatures
• classes/apidata.py supports OAC_BACKEND / OAC_DB_PATH and sqlite backend detection
• classes/query_service.py encapsulates API-compatible query execution for MCP and tests
• mcp_server.py exposes query_api and supporting MCP resources
• docker-compose.yml, Dockerfile.api, Dockerfile.mcp, Dockerfile.ingest, .env.example, and docs/deployment-compose.md provide constrained-host deployment path
• classes/compat.py provides local is_integer / is_number helpers to replace astrocats.catalog.utils

Validation

• python3 -m unittest tests/test_migration_smoke.py
• python3 -c "import api; print('api-import-ok')"

Notes

• TNS-related messages and handlers were removed per requirement to avoid external-service interaction.
• Existing API signatures are preserved; backend behavior is controlled via environment configuration.
• No GitHub fallback is used for event files; full queries rely on local event JSON files only.